feat: initial Dialectic.OpenclawPlugin — agent tools for Dialectic v2

Phase 3 of DIALECTIC-V2. Six tools wired to the Go backend running on
server.t3:

- dialectic_list_topics      GET  /api/topics
- dialectic_topic_detail     GET  /api/topics/{id}
- dialectic_propose_topic    POST /api/topics
- dialectic_signup           POST /api/topics/{id}/signups (HF pre-check)
- dialectic_post_argument    POST /api/topics/{id}/arguments
- dialectic_view_verdict     GET  /api/topics/{id}/verdict

All tools return MCP {content:[{type:text,text}]} shape. Errors caught
and surfaced as text payload so agents see actionable failure messages.

Per-agent API key resolved via secret-mgr key dialectic-agent-apikey
(cached in memory; AGENT_VERIFY env required). HF on_call coverage
check degrades gracefully to skipped if HarborForge.OpenclawPlugin
does not yet expose hasOnCallCovering() — backend stores pre_validated
flag as audit signal.

openclaw.plugin.json declares both contracts.tools (the 6 names) AND
activation.onStartup:true per loader gotchas memory; missing either
silently drops the plugin.

Plain export default {id, name, register} entry shape matching
prism-facet. No openclaw SDK imports (jiti runtime resolution of
openclaw was flaky in HF-style entries; structurally simpler avoids
the lookup entirely).

Defaults backendUrl to https://dialectic-api.hangman-lab.top; override
via openclaw.json plugins.entries.dialectic.config.backendUrl for sim.

Phase 3 deferred items (in README): agent key provisioning workflow,
HF window-coverage accessor, SSE subscription tool, token-cost
reporting.

plugin/openclaw.plugin.json

@@ -0,0 +1,31 @@
+{
+  "id": "dialectic",
+  "name": "Dialectic",
+  "version": "0.1.0",
+  "description": "OpenClaw plugin for the Dialectic v2 debate platform — agent-facing tools",
+  "main": "index.js",
+  "activation": {
+    "onStartup": true
+  },
+  "contracts": {
+    "tools": [
+      "dialectic_list_topics",
+      "dialectic_topic_detail",
+      "dialectic_propose_topic",
+      "dialectic_signup",
+      "dialectic_post_argument",
+      "dialectic_view_verdict"
+    ]
+  },
+  "configSchema": {
+    "type": "object",
+    "additionalProperties": false,
+    "properties": {
+      "backendUrl": {
+        "type": "string",
+        "description": "Dialectic backend base URL (e.g. https://dialectic-api.hangman-lab.top)",
+        "default": "https://dialectic-api.hangman-lab.top"
+      }
+    }
+  }
+}